Session Effect of Washing Cellulose Triacetate Films with Different Degrees of Degradation

Presenter

 Karin Bonde Johansen
Danish Film Institute


ABSTRACT

An investigation of the effects of washing motion picture film in water and 0.1 M sodium acetate. New cellulose triacetate films were used for the experiment. Six types of samples were tested. A batch of acetate film (Orwo) was produced with and without emulsion. Three samples from each were made consisting of new films, slightly aged films and highly aged films (artificially aged at 90 oC and 50 % RH). The different samples were washed and afterwards incubated at 60 oC and 50 % RH for 10 months. Sampling was done every month and Water-Leach Free Acidity Test, infrared spectroscopy (ATR-FTIR) and shrinkage were used to examine the results. There is an initial indication of lower acidity in the films washed with sodium acetate, if the treatment was performed just before the film reached the autocatalytic point.  The presentation will examine the test results for statistical significance and conclusions.

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PRESENTATION

Introduction
The effect of aqueous treatment of motion picture films of cellulose triacetate (CA) is today largely unknown. Motion picture film is washed several times during its lifetime. New films are rinsed in water after development; original negatives might be washed several times during cutting before the final duplication, old screening copies are rewashed to reduce scratches and degraded films with vinegar syndrome are washed to decrease the generation of acetic acid (Johansen, 2004, p. 1).

Experiments were performed in order to investigate the effect of washing both new films, slightly degraded films and highly degraded films. The films were washed in either water or in a basic solution.

The wash in water was performed to investigate if aqueous treatments of films performed today increase or decrease the degradation over time.

The wash in a basic solution was performed to investigate the possibility of incorporation of a base in the film to neutralize acetic acid generated later on in the degradation of the film. If a basic wash could delay the degradation of the film, it might be useful as an active conservation treatment, which today is not available. Duplication of degraded films is the only way to save the films. But the quality of the duplication might not be as good as the original image, and duplication is both time-consuming and expensive. Therefore, treatments to prolong the lifetime of the original film material are highly recommendable.

The project was a cooperation between the Danish Film Institute and the National Museum of Denmark and financially supported by the Danish Ministry of Culture.

Experimental
Thirty-five mm black and white motion picture films of cellulose triacetate from ORWO were used as the test material for the experiments. To investigate the role of the emulsion in the degradation process, both films with emulsion and films without emulsion were included. The test material was divided into 54 rolls of each 30 metres. To obtain test material with different degrees of degradation, one third of the test material was slightly pre-aged and one third was highly pre-aged. The pre-ageing was performed at 90º C. Altogether, the treatments were performed for six different groups of films:

1. New films with emulsion
2. Slightly pre-aged films with emulsion
3. Highly pre-aged films with emulsion
4. New films without emulsion
5. Slightly pre-aged film without emulsion
6. Highly pre-aged film without emulsion

The rolls were washed in either tap water or in a basic solution of 0.1 M sodium acetate, CH3COONa. The wash was carried out in a processing machine for microfilms , and the speed of the machine resulted in total immersion of the film in the aqueous solution (water or 0.1 M sodium acetate) for 1½ minute. The temperature of the aqueous solutions was 20º C ± 2º C. The rolls washed in water were transported though three chambers of the processing machine with constantly shifting water. The rolls treated in 0.1 M sodium acetate were run though one chamber of water, one chamber of 0.1 M sodium acetate and rinsed in one chamber of water. Subsequently, the rolls were moisture conditioned for three weeks in approximately 50 % relative humidity. To maintain constant moisture content in the film rolls during accelerated ageing, the rolls were packed in airtight aluminium bags coated inside with polyethylene.

The rolls were accelerated aged at 60º C at most for 10 months.

Measurements
The Water-Leach Free Acidity Test (Adelstein et al., 1995, p. 291) measures the film acidity and was the main test method for monitoring the result of these experiments . Small pieces of one gram of film are leached into water, stirred at 38º C for 24 hours and filtrated. The solution is titrated with 0.1 M NaOH and the acidity value is expressed as millilitre of 0.1 M NaOH. Duplicate measurements were made for each sample.

Results, comments and discussion
The results of the experiments are shown in Figure 1 to Figure 7.

New films with emulsion showed a beneficial effect of the wash (Figure 1) after accelerated ageing at 60º C. The untreated sample has generated more acid after 10 months of incubation, than the sample washed in water and the sample washed in 0.1 M sodium acetate. According to these experiment it seems that various aqueous treatments performed at news films don't increase the rate of degradation, in fact it seems that aqueous treatments improve the stability of the film. There is no difference in the effect of the treatments between wash in water and wash in 0.1 M sodium acetate.

Conclusion
The effect of washing motion picture films after accelerated aging at 60 ?C both was positive and negative:

New films: Washing new films gave a positive result. Treated samples generated less acid compared with an untreated sample after aqueous treatment for one and a half minute (Figure 1). According to these experiments, wash of new films in either water or 0.1 M sodium acetate will slightly improve the stability over time.

Slightly degraded films: Washing slightly degraded films gave both a positive and a negative result. The stability of films accelerated pre-aged to AD-level = 0.5 at 90 ?C was decreased after aqueous treatment for one and a half minute (Figure 2), where the stability of naturally aged film also reacting to AD-level = 0.5 at the time of the treatment was increased after aqueous treatment for ten minutes (Figure 4).
The answer to washing or not washing slightly degraded films is therefore not clear. However, due to the results of the naturally aged samples after wash in ten minutes, I will not deprecate to rewash a film in order to reduce scratches, if it makes the film useable again. Considerations of advantages and disadvantages in each case must been done.

Highly degraded films: Washing highly degraded film (accelerated pre-aged at 90 ?C) showed a negative result. Samples washed in water resulted in slightly higher acidity values compared with an untreated sample.

Considerations in each case must be done whether to wash or not to wash. Automatically washing of all films with vinegar syndrome do not seems to increase the stability of the film, but there might be cases where a wash could make the film useable for a short time.

It was not possible to incorporate an alkaline reserve in film in order to delay further degradation. Nevertheless, a positive effect was found for samples without emulsion washed in 0.1 M sodium acetate, if washed just before occurrence of the autocatalytic point. The reason for this positive effect is unknown.

The role of the emulsion was investigated and it was found that the emulsion both played a negative and positive role in the degradation of cellulose acetate. Further research of degradation of gelatine emulsion is needed to fully understand the degradation processes of the emulsion.

References
Adelstein, P. Z. & McCrea, J.L. (1981) Stability of Processed Polyester Base Photographic Films, J. of Appl. Photogr. Eng. 7, pp. 160-167.

Adelstein, P. Z., Reilly, J. L., Nishimura, D. W. & Erbland, J. (1992) Stability of Cellulose Ester Base Photographic Film: Part I - Laboratory Testing Procedures, SMPTE Journal, May, p. 336-346.

Adelstein, P. Z., Reilly, J. L., Nishimura, D. W. & Erbland, J. (1995) Stability of Cellulose Ester Base Photographic Film: Part III - Measurement of the Film Degradation, SMPTE Journal, May, p. 281-291.

Allen, N.S., Edge, M., Appleyard, J.H., Jewitt, T.S., Horie, C.V. & Francis, D. (1988b) Acid-Catalysed Degradation of Historic Cellulose Triacetate Cinematographic Film: Influence of Various Film Parameters, J. of European Polymer, Vol. 24, No. 8, pp. 707-712.

Balany, J. (2000) An Investigation of the Factors Affecting the Degradation of Cellulose Acetate Artefacts in Museum Collections. PhD. University of Strathclyde.

Egde, M. (1994) Factors Influencing the Breakdown of Photographic Film: Implications for Archival Storage, Invironnement et Conservation de l'Ècrit, de l'Image et du son, Actes des Deuxièmes Journées Internationales d'Études de l'Arsag, Paris 16-20 Mai, pp. 100-120.

Johansen, K.B. (2004) Effect of Washing Cellulose Triacetate Films with Different Degrees of Degradation. Master Thesis, The Royal Danish Academy of Fine Arts, School of Conservation, Copenhagen, 148 pp.

Reilly, J.M. (1993a) IPI Storage guide for Acetate Film, Image Permanence Institute, Rochester Institute of Technology, Rochester, New York.

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SPEAKER BIO

Karin Bonde Johansen is M.A. in conservation from The Royal Danish Academy, The School of Conservation. Since 1999, she is a film archivist at the Danish Film Institute, and in 2001, she participated The L. Jeffrey Selznick School of Film Preservation, George Eastman House, Rochester, USA for 5 weeks. Additionally, she has been teaching in film conservation at The Royal Danish Academy, The School of Conservation in Copenhagen.